Many joinery elements such as frames, framework, jambs and transoms of windows, shutters, doors and gates are frequently formed based on PVC (polyvinyl chloride), which gives them durability, corrosion resistance and thermal insulating properties, while requiring only a minimum amount of maintenance. However, they lack rigidity from certain dimensions onwards.
Indeed, the PVC profiles used for the construction of these joinery elements are generally hollow in order to lighten them and create chambers that have a thermal insulation role. However, one problem inherent to PVC is its low elastic modulus and therefore its deformability under strain, especially when the spans between fixed points are large.
The lack of rigidity may be overcome by reinforcing the frames with metal reinforcements and especially steel (see document DE 199 33 099) or aluminium reinforcements. However, the use of metal reinforcements creates thermal bridges within the profiles of the frame leading to significant heat losses via the increase of the thermal conductivity. Furthermore, the presence of these metal reinforcements complicates the end-of-life recycling of the profiles.
In order to counteract this increase of the thermal conductivity, it has been proposed to use reinforcements (pultruded inserts) constituted of thermosetting resins with fibres, preferably continuous fibres, of glass, aramid or carbon (documents GB 2 144 472 or EP 0 441 449). However, the use of thermosetting resins with glass fibres is expensive. As regards the thermoplastic composite materials reinforced by cellulose fibres described in document US 2004/062915, they are much more moisture-sensitive and therefore less durable.
Conventionally, PVC profiles reinforced by introduction of a metal insert or of a pultruded insert are not recyclable or are difficult to recycle. Another disadvantage of profiles reinforced by a pultruded insert is the fact that it is necessary, just like for metal reinforcements, to manually introduce the reinforcement, which increases their production cost.
Described in document EP 1 276 602 are joinery elements comprising a PVC profile reinforced by at least one reinforcing tape composed of fibres made of polyester, in particular made of PET (polyethylene terephthalate) or of PBT (polybutylene terephthalate) commingled with continuous glass fibres; the polymer fibres and glass fibres being arranged in a longitudinal and parallel manner. The tapes of fibres, or rovings, are heated in order to melt the polymer, pressed and finally embedded in the outer and opposite walls of the final PVC profile to provide sufficient rigidity and thus avoid the use of metal or pultruded inserts. Even though high mechanical properties are obtained and the manual insertion of the metal or pultruded profile is avoided owing to the manufacturing process which uses reels that make it possible to unwind continuous yarns comprising continuous filaments of glass and of a thermoplastic commingled together, this process has many disadvantages. One of the drawbacks of this system is combining two different thermoplastics that are incompatible in the melt state, a polyester such as PET or PBT on the one hand and PVC on the other hand, in the final product, making not only the recycling of the profile difficult, but also making the recycling of the production scrap and also of the blanks impossible in the production line of the profiles. Another drawback is the longitudinal brittleness of the reinforcements which preferably break along the fibres during a multiaxial impact. Finally, one major drawback is the difficulty in calibrating the profile when it is cooling considering that the PVC and the reinforcing tape have different thermal expansion coefficients.
In document EP 0 179 688, it has been proposed to subject reinforcing elements (especially glass fibres) for composite materials to an electrostatic field induced by a very high voltage electric current, then to impregnate them with a liquid matrix material (or liquid precursor of the material), while they are still under the influence of the field. The very high voltages that must be used in order to carry out this process are not without danger for the operators and require a lot of electrical energy; it is not easy either to correctly synchronize the swelling of the reinforcing fibres under the action of the electrostatic field and their impregnation by the liquid matrix material.